System and method for transmitting communication signals to an automated robotic device in a data storage system

ABSTRACT

A system and method for transmission of communication signals between a controller and a robotic device in a data storage library. The system and method include a substantially planar electrical insulator having opposed first and second sides, and first and second substantially planar oppositely charged electrical conductors on the first and second sides of the insulator for use in providing electrical power to the robotic device. The system and method also include circuitry for generating the communication signals for transmission between the controller and the robotic device on one of the first and second conductors. The width of the second conductor is less than the width of the first conductor and the second conductor is substantially centered on the second side of the insulator relative to the width of the first conductor to reduce fringing of an electromagnetic field resulting from a transmitted communication signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisionalapplication Serial No. 60/302,248 filed Jun. 29, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to the transmission ofcommunication signals in a data storage system and, more particularly,to a system and method for transmitting communication signals between acontroller and an automated robotic device in a tape cartridge librarysystem.

[0004] 2. Background

[0005] Current automated libraries for tape cartridges typically includearrays of multiple storage cells housing the tape cartridges, as well asmultiple media drives. Multiple automated robotic devices may be used tomove tape cartridges between the various storage cells and media driveswithin a library.

[0006] The use of multiple robotic devices in automated tape cartridgelibraries raises various problems concerning the distribution of powerto such robotic devices. More particularly, robotic devices used inautomated tape cartridge libraries require power for operation thereof.In prior art automated tape cartridge libraries, the movement of therobotic devices is restricted by wire cable connections used forproviding such power. That is, such cabling can prevent the roboticdevices from crossing paths, or from continuous movement in onedirection around the library without the necessity of ultimatelyreversing direction.

[0007] Such problems can be overcome through the use of brush/wipertechnology. A robotic device traveling over a given route may use apower distributor such as fixed conductive strips to supply power to therobotic device, which itself is provided with brushes or wipers thatcontact the conductive strips in order to conduct power to the roboticdevice. Multiple brushes are preferably used on each robotic device toimprove robustness and reliability. The integration of such conductivestrips into the automated tape cartridge library, in conjunction withbrush contacts provided on the robotic devices, allows for greaterfreedom of movement of the robotic devices, as well as for modular andextensible power distribution to robotic devices as libraryconfigurations change, or as libraries are connected in a modularfashion to form library systems.

[0008] Advantageously, the oppositely charged conductive layers of apower strip as described above can be used for transmittingcommunication signals between the robotic device and a host controller.In doing so, however, electromagnetic interference and unintended signalemissions can be a problem. This can be particularly true for powerconductors that are quite long. Interference from radio, television, andother radio frequency (RF) electromagnetic radiation sources, whether ornot intentionally emitted, can interfere with the communication signalsmodulated onto the power conductors. Such interference can cause datatransmission errors and slow the maximum attainable rate of datatransfer.

[0009] In that same regard, when communication signals are modulatedonto a long power conductor, some of the RF energy can radiate throughthe air and interfere with nearby independent power conductors. If thenearby power conductors also contain modulated communication signals,harmful interference can result. The energy radiated by the modulatedpower conductors may also cause interference in radio and televisionbroadcast bands, or other restricted RF bands. Such interference may beprohibited by government regulations.

[0010] Thus, there exist a need for an improved system and method fortransmitting communication signals between a controller and a roboticdevice in a data storage library. Such a system and method would improvethe electromagnetic compatibility (EMC) of brush and strip powerdistribution by the orientation of the power strip conductors. Moreparticularly, such an improved system and method would employ positiveand negative (ground) conductors preferably separated by a thin layer ofinsulating dielectric. The positive conductor would preferably becentered over the negative conductor, and the negative conductor wouldpreferably be wider than the positive conductor in order to minimizefringing of the electric filed due to the modulated communicationsignal. The thin dielectric would minimize the “loop area” of theconductors. The conductors themselves would be substantially flat andrelatively thin in order to reduce their respective surface areas,thereby reducing “skin effect.”

SUMMARY OF THE INVENTION

[0011] Accordingly, the present invention provides an improved systemand method for transmitting communication signals to and from anautomated robotic device for use in a data storage library.

[0012] According to the present invention, then, in a data storagelibrary having a plurality of cells for holding media cartridges for usein storing data, at least one media drive, a robotic device fortransporting cartridges between the plurality of cells and the at leastone media drive in the data storage library, and a controller forcontrolling the robotic device, a system is provided for transmission ofcommunication signals between the controller and the robotic device. Thesystem comprises a substantially planar electrical insulator havingopposed first and second sides, a first substantially planer electricalconductor on the first side of the insulator for use in providingelectrical power to the robotic device, the first conductor to beprovided with an electrical charge and having a width, and a secondsubstantially planar electrical conductor on the second side of theinsulator for use in providing electrical power to the robotic device,the second conductor to be provided with an electrical charge oppositethe electrical charge of the first conductor, the second conductorhaving a width. The system further comprises means for generating thecommunication signals for transmission between the controller and therobotic device on one of the first and second conductors, wherein thewidth of the second conductor is less than the width of the firstconductor, and the second conductor is substantially centered on thesecond side of the insulator relative to the width of the firstconductor to reduce fringing of an electromagnetic field resulting froma transmitted communication signal.

[0013] Also according to the present invention, in a data storagelibrary having a plurality of cells for holding media cartridges for usein storing data, at least one media drive, a robotic device fortransporting cartridges between the plurality of cells and the at leastone media drive in the data storage library, and a controller forcontrolling the robotic device, a method is provided for transmission ofcommunication signals between the controller and the robotic device, themethod comprises providing a substantially planar electrical insulatorhaving opposed first and second sides, providing a first substantiallyplaner electrical conductor on the first side of the insulator for usein providing electrical power to the robotic device, the first conductorto be provided with an electrical charge and having a width, andproviding a second substantially planar electrical conductor on thesecond side of the insulator for use in providing electrical power tothe robotic device, the second conductor to be provided with anelectrical charge opposite the electrical charge of the first conductor,the second conductor having a width. The method further comprisesproviding means for generating the communication signals fortransmission between the controller and the robotic device on one of thefirst and second conductors, wherein the width of the second conductoris less than the width of the first conductor, and the second conductoris substantially centered on the second side of the insulator relativeto the width of the first conductor to reduce fringing of anelectromagnetic field resulting from a transmitted communication signal.

[0014] The above features, and other features and advantages of thepresent invention are readily apparent from the following detaileddescriptions thereof when taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a robotic device for use in anautomated tape cartridge library having brush and strip powerdistribution;

[0016]FIGS. 2a and 2 b are partial cross-sectional views of a roboticdevice for use in an automated tape cartridge library having brush andstrip power distribution;

[0017]FIG. 3a is a simplified block diagram of a robotic device for usein an automated tape cartridge library according to the prior art;

[0018]FIG. 3b is a simplified a block diagram of a robotic device foruse in an automated tape cartridge library having brush and strip powerdistribution;

[0019]FIGS. 4a and 4 b are simplified overhead block diagrams of a powerstrip and robotic device with conductive brushes for use in an automatedtape cartridge libraries;

[0020]FIGS. 4c and 4 d are simplified electrical schematics depictingpower supply redundancy schemes according to the present invention;

[0021]FIG. 5 is a perspective view of a robotic device for use in anautomated tape cartridge library having brush and wheel powerdistribution;

[0022]FIG. 6 a more detailed perspective view of a robotic device foruse in an automated tape cartridge library having brush and wheel powerdistribution;

[0023]FIG. 7 is another more detailed perspective view of a roboticdevice for use in an automated tape cartridge library having brush andwheel power distribution;

[0024]FIGS. 8a and 8 b are side and cross-sectional views, respectively,of a brush and wheel mechanism for power distribution to a roboticdevice in an automated tape cartridge library;

[0025]FIG. 9 is an exploded perspective view of power strip and guiderail joint for use in an automated tape cartridge library;

[0026]FIG. 10 is a perspective view of a power strip joint for use in anautomated tape cartridge library;

[0027]FIGS. 11a and 11 b are additional perspective views of a powerstrip joint for use in an automated tape cartridge library;

[0028]FIGS. 12a and 12 b are perspective views of a guide rail sectionsfor use in an automated tape cartridge library having brush and strippower distribution;

[0029]FIGS. 12c-g are cross-sectional and side views of a power stripand guide rail assembly for use in an automated tape cartridge library;

[0030]FIG. 13 is a simplified block diagram illustrating distribution ofcommunication signals to and from robotic devices for use in anautomated tape cartridge library according to the present invention;

[0031]FIG. 14 is a cross-sectional view of a power strip and conductivebrushes for use in an automated tape cartridge library according to thepresent invention;

[0032]FIG. 15 is a top view of a power strip for use in an automatedtape cartridge library according to the present invention;

[0033]FIGS. 16a and 16 b are a cross-sectional view and a simplifiedelectrical schematic, respectively, of a power strip for use in anautomated tape cartridge library according to the present invention;

[0034]FIG. 17 is a simplified electrical schematic diagram illustratinga termination scheme for a line in a power strip or rail communicationsystem according to the present invention;

[0035]FIG. 18 is a simplified, exemplary flowchart depicting the methodof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0036] With reference to the Figures, the preferred embodiments of thepresent invention will now be described in greater detail. The presentapplication incorporates by reference herein commonly owned U.S. patentapplication Nos. ______ (Attorney Docket No. 2001-043-TAP), ______(Attorney Docket No. 2001-047-TAP), ______ (Attorney Docket No.2001-048-TAP), ______ (Attorney Docket No. 2001-049-TAP), and ______(Attorney Docket No. 2001-100-TAP), all filed on the same date as thepresent application.

[0037] As previously noted, current automated libraries for tapecartridges typically include arrays of multiple storage cells housingthe tape cartridges, as well as multiple media drives. Multipleautomated robotic devices may be used to move tape cartridges betweenthe various storage cells and media drives within a library.

[0038] As also noted previously, the use of multiple robotic devices inautomated tape cartridge libraries raises various problems concerningthe distribution of power to such robotic devices. More particularly,robotic devices used in automated tape cartridge libraries require powerfor operation thereof. In prior art automated tape cartridge libraries,the movement of the robotic devices is restricted by wire cableconnections used for providing such power. That is, such cabling canprevent the robotic devices from crossing paths, or from continuousmovement in one direction around the library without the necessity ofultimately reversing direction.

[0039] Such problems can be overcome through the use of brush/wipertechnology. A robotic device traveling over a given route may use apower distributor such as fixed conductive strips or rails to supplypower to the robotic device, which itself is provided with brushes orwipers, or wheels and brushes that contact the conductive strips orrails in order to conduct power to the robotic device. Multiple brush orwheel pairs are preferably used on each robotic device to improverobustness and reliability. The integration of such power distributors,which also may be referred to as power distribution strips or powerdistribution rail assemblies, into the automated tape cartridge library,in conjunction with brush or wheel contacts provided on the roboticdevices, allows for greater freedom of movement of the robotic devices,as well as for modular and extensible power distribution to roboticdevices as library configurations change, or as libraries are connectedin a modular fashion to form library systems.

[0040]FIGS. 1 and 2a-b show perspective and cross-sectional views,respectively, of a robotic device for use in an automated tape cartridgelibrary having brush and strip power distribution. As seen therein, amoveable robotic device (20), which may be referred to as a “handbot” or“picker,” is supported by a guide structure or rail (2) preferablyhaving an integrated power strip (1). Guide rail (2) and/or power strip(1) may also be referred to as a track. Power strip (1) preferablycomprises back-to-back conductive surfaces (1A, 1B), preferably copper,separated by a dielectric (preferably FR4) in a sandwich-likeconfiguration. As described in greater detail below, such aconfiguration provides for improved impedance control. Power strip (1)may be a printed circuit board wherein copper conductors are laminated,glued or etched onto a substrate material. Alternatively, power strip(1) may comprise copper foil tape glued or laminated onto plasticmaterial, or copper inserts molded into a moldable plastic material. Anyother methods of construction or configurations known to those ofordinary skill may also be used.

[0041] Robotic device (20) includes brush contacts (6) for providingpower to robotic device (20). In that regard, the back-to-backconductive surfaces (1A, 1B) of power strip (1) are oppositely charged.An upper brush (6A) in contact with one conductive surface (1A), inconjunction with a corresponding lower brush (6B) in contact with theopposite conductive surface (1B) thereby supply power to the roboticdevice (20). Brushes (6) are contained in housing assembly (7) and, toensure that contact between brushes (6) and power strip (1) ismaintained, brushes (6) are spring loaded (8). Multiple or redundantpairs of such upper and lower brushes (6) are preferably provided, andpreferably spring loaded (8) independently, to improve robustness andreliability in the event of a brush failure, momentary loss of contactat one or more brushes due to any track irregularities, including seamsor joints therein, or voltage irregularities between adjacent powerstrips (1). Moreover, brushes (6) preferably have a circularcross-section, such as is provided by a cylindrical shaped brush (6), asthese are better able to traverse a joint or seam (38) in the powerstrip (1), which may more readily impede or catch a square shaped brush.

[0042] Power supplied to robotic device (20) through power strip (1) andbrushes (6) powers a motor (not shown) in robotic device (20), which inturn drives a belt and gear system (22). Guide rails (2) includes teeth(24) which cooperate with belt and gear system (22) to permit roboticdevice (20) to move back and forth along guide rails (2) via guidewheels (26). In that regard, it should be noted that power strip (1)preferably provides DC power to robotic device (20). As seen in FIG. 1,robotic device (20) may thereby gain access to tape cartridges stored inlibrary cells (28) located adjacent guide rail (2). It should also benoted that while only a single robotic device (20) is depicted, powerstrip (1) is preferably suitable, according to any fashion known in theart, to provide power to multiple robotic devices. In that regard, eachrobotic device (20) is suitably equipped with a circuit breaker (notshown) in any fashion known in the art in order to isolate the roboticdevice (20) from the power strip (1) in the event that the roboticdevice short circuits. In such a manner, the failure of the entire powerstrip (1) is prevented.

[0043] Referring now to FIG. 3a, a simplified block diagram of a roboticdevice for use in an automated tape cartridge library according to theprior art is shown. As seen therein, a prior art robotic device (30) inan automated tape cartridge library has a pair of spaced apart,oppositely charged power rails (32). The robotic device (30) is providedwith a pair of brush contacts (34) for supplying power from two powerrails (32) to the robotic device (30), in order to allow movement of therobotic device (30). As seen in FIG. 3a, the large distance, x, betweena cooperating pair of brushes (34) creates uneven wear on the brushes(34) due to construction tolerances in the robotic device (30) and thetrack or power rails (32). Brushes (34) also causes uneven drag on therobotic device (30) by creating a moment load resulting from theseparation, x, between the brush (34) and power rail (32) frictionpoints.

[0044]FIG. 3b is a simplified a block diagram of a robotic device foruse in an automated tape cartridge library having brush and strip powerdistribution. As seen therein, in contrast to the prior artconfiguration of FIG. 3a, power is supplied to the robotic device (20)through the power strip (1) and brush (6) configuration described inconnection with FIGS. 1 and 2a-b, thereby facilitating the eliminationof the large separation between a pair of cooperating brushes (6A, 6B),and the accompanying problems, and allowing for lower constructiontolerance requirements. The single rail construction, two-sided powerstrip (1) and brush (6) configuration also acts to reduce costs andprovides for a more integrated assembly. As seen in FIG. 3b, anoptional, non-powered lower guide rail (36) may also be provided forrobotic device (20). It should also be noted that the copper foil tapethat may be used in the construction of the power strip (1) may beinstalled in the field during the assembly of the automated tapecartridge library. In such a fashion, it may be possible to eliminateall electrical joints in power strip (1) by using a continuous copperfoil strip.

[0045]FIGS. 4a and 4 b are simplified overhead block diagrams of a powerstrip (1) and robotic device (20) with conductive brushes (6) for use inan automated tape cartridge libraries according to the presentinvention. As seen in FIG. 4a, power strips (1) may be fed power fromboth ends thereof, or multiple sections of power strips may be fed fromboth ends. Robotic device (20) is preferably provided with multiplepairs of cooperating brush contacts (6), only the top brushes in eachcooperating pair being visible in FIG. 4a. In that regard, withreference again to FIGS. 2a and 2 b, it should also be noted that brushpairs on each side of power strip (1) are oriented so as to follow thesame path. That is, a pair of brushes (6) contacting the same conductivesurface (1A, 1B) are aligned so that both such brushes (6) contact thesame part of the conductive surface (1A, 1B) as robotic device (20)moves in the library. Such a brush orientation facilitates the creationof a beneficial oxide layer on the conductive surfaces (1A, 1B). As willbe discussed in greater detail below, such an oxide layer helps reduceboth electrical and sliding resistance between the brushes and theconductive surfaces (1A, 1B).

[0046] Referring still to FIGS. 4a and 4 b, cooperating brush pairs arepreferably spaced apart on robotic device (20). Such spacing, as well asthe use of multiple cooperating brush pairs provides for greaterrobustness and freedom of movement for robotic device (20) in the eventof track irregularities, including unevenness or “dead” track sections.In that regard, as seen in FIG. 4a, a non-powered or “dead” section (40)of power strip (1) will not necessarily prevent robotic device (20) fromtraversing the full extent of the power strip (1). That is, as therobotic device (20) moves across the dead track section (40), onecooperating pair of brushes always maintains contact with a poweredtrack section (42, 44). Similarly, as seen in FIG. 4b, power strip (1)may be fed power from a more centralized region thereof. As a result ofthe separation of cooperating pairs of brush contacts, robotic device(20) may be able to traverse longer distances than the length of powerstrip (1) onto and off of non-powered end-of-track sections (46, 48),provided at least one cooperating pair of brushes maintain contact withpowered track section (50). Moreover, in such a fashion, non-poweredtrack sections may be provided where a robotic device (20) may bedeliberately driven off power strip (1) and thereby powered down forservice.

[0047] In that same regard, FIGS. 4c and 4 d depict simplifiedelectrical schematics of power supply redundancy schemes. As seen inFIG. 4c, in a brush and strip power distribution system, failure of apower supply (150) or a break (152) in the electrical continuity in apower strip (1) will cause a power interruption. Such an electricaldiscontinuity (152) in turn will result in a loss of power to all of therobotic devices (20 i, 20 ii, 20 iii, 20 iv) connected to the conductor.More specifically, such an electrical break (152) will result in theloss of power to those devices (20 iii, 20 iv) located on thedisconnected side (154) of the strip (1). As will be described ingreater detail below, a brush a strip power distribution system may beimplemented using many interconnected segments or sections to createpower strip (1). Each interconnect substantially increases thepossibility that power to part or all of the power strip (1) may beinterrupted.

[0048] The present design substantially improves the reliability of sucha power distribution system by ensuring that the failure of a singlepower supply or an electrical break in power strip (1) will notinterrupt operation of the automated robotic library. More specifically,as seen in FIG. 4d, the present invention preferably provides forconnecting two power supplies (150 i, 150 ii), rather than one, to powerstrip (1). In the preferred embodiment shown in FIG. 4d, the two powersupplies (150 i, 150 ii) are positioned at the two ends of power strip(1), and electrically connected to both ends of power strip (1). Thepower supplies (150 i, 150 ii) are preferably of the redundant/loadsharing type.

[0049] When both supplies (150 i, 150 ii) are active and functioningnormally, they share the load created by robotic devices (20 i, 20 ii,20 iii, 20 iv) nearly equally. In the event, however, that one powersupply (e.g., 150 i) fails, the remaining power supply (e.g., 150 ii)automatically begins to source power to all of the devices (20 i, 20 ii,20 iii, 20 iv) connected to the power strip (1). Moreover, in the eventof an electrical discontinuity or break (152) in the power strip (1),each power supply (150 i, 150 ii) will continue to deliver power to thedevices (20 i, 20 ii, 20 iii, 20 iv) located on that power supply's (150i, 150 ii) respective side of the break (152). Alternatively, as shownin dashed line fashion in FIG. 4c, single power supply (150) may beconfigured to supply power to both ends of power strip (1), therebyensuring that a break (152) in power strip (1) will not result in lossof power to any of robotic devices (20 i, 20 ii, 20 iii, 20 iv). Itshould be noted that while shown in FIGS. 4c and 4 d as electricallyconnected at the ends of power strip (1), power supplies (150, 150 i,150 ii) may alternatively and/or additionally be electrically connectedto any other point or points on power strip (1). That is, in a powerstrip (1) comprising a plurality of electrically interconnected sectionsor segments, power supplies (150, 150 i, 150 ii) may be electricallyconnected to any number of sections anywhere along power strip (1). Itshould also be noted that the power supply redundancy schemes depictedin FIGS. 4c and 4 d are equally suitable for use in the brush and wheelpower distribution system described in detail immediately below.

[0050] Referring next to FIGS. 5 through 8a and 8 b, variousperspective, side and cross-sectional views of a robotic device for usein an automated tape cartridge library having brush and wheel powerdistribution. As seen therein, in this alternative embodiment, roboticdevice (20) is supported by a guide rail (2), which is provided with apair of oppositely charged power conductors (3), preferably in the formof copper rails. Power rails (3) supply power to robotic device (20)through power transmission carriage assembly (4). Power supplied torobotic device (20) via power rails (3) and power transmission carriage(4) powers a motor (not shown), which in turn drives belt and gearmechanism (22) to permit robotic device (20) to move back and forthalong guide rail (2) via guide wheels (26). In that regard, it should benoted that power rails (3) may provide either AC or DC power to roboticdevice (20). It should also be noted again that while only a singlerobotic device (20) is depicted, power rails (3) are preferablysuitable, according to any fashion known in the art, to provide power tomultiple robotic devices. As described above in connection with thebrush and strip power distribution, each robotic device (20) is suitablyequipped with a circuit breaker (not shown) in any fashion known in theart in order to isolate the robotic device (20) from the power rails (3)in the event that the robotic device short circuits. In such a manner,the failure of the power rails (3) is prevented.

[0051] Power transmission carriage (4) includes multiple cooperatingpairs of conduction wheels (5) (preferably copper), the individualmembers of a cooperating pair provided in contact, respectively, withoppositely charged conductor rails (3). Conductive brushes (10) areprovided to contact conduction wheels (5) and are spring loaded (11),preferably independently, to maintain such contact. To maintain contactbetween conduction wheels (5) and conductor rails (3), powertransmission carriage (4) also includes vertical pre-load spring (6).Power transmission carriage (4) still further includes gimbal arm (7)with pivot shaft (8) and pivot screw (9) for carriage compliance. Onceagain, multiple or redundant conduction wheel (5) and conductive brush(10) pairs are preferably provided, and preferably spring loaded (11)independently, to improve robustness and reliability in the event of abrush failure, momentary loss of contact at one or more wheels due toany track irregularities, including seams or joints therein, or voltageirregularities between adjacent power rails (3). In that same regard,while a single vertical pre-load spring (6) is shown, each conductionwheel (5) could also be independently spring loaded to maintain contactwith conductor rails (3), thereby allowing for better negotiation of anytrack irregularities or imperfections, including joints or seams.

[0052] The brush and wheel embodiment can reduce particulate generationwhich may accompany the brush and power strip embodiment as a result ofbrushes negotiating imperfectly aligned track joints. Moreover, becauseof the more contained nature of the contact between a brush and wheel asopposed to between a brush and extended power strip, any suchparticulate generation can be more easily contained in the brush andwheel embodiment, such as through the use of a container (not shown)surrounding the brush and wheel to capture any particulate. The brushand wheel embodiment also provides for improved negotiation of joints bya robotic device as it provides for wheels rolling rather than brushessliding over a joint. As a result, less strict tolerances are requiredfor joint design and assembly. Moreover, a brush passing over anirregularity in a power strip, such as a joint, scrapes both the brushand the track, causing wear to both. A wheel can more easily negotiatesuch irregularities, thereby reducing such wear.

[0053] The brush and wheel embodiment also provides for reducedelectrical and sliding resistance as compared to the brush and stripembodiment. In that regard, a beneficial oxide layer that reduces bothelectrical and sliding resistance develops more easily and quicklybetween a brush and wheel contact than between a brush and extendedpower strip contact, again because of the more contained nature of thecontact. That is, for a given linear movement of a robotic device, abrush covers much more of the surface, and much of the same surface of awheel than it covers on an extended linear conductive strip. This isparticularly advantageous in reducing high brush resistance when therobotic device is traveling at low speeds.

[0054] The brush and wheel embodiment also generally reduces the springloading forces required. In that regard, because of irregularities in aconductive strip, such as due to joints or seams, a high spring loadingforce is required to ensure contact is maintained between a brush andpower strip, particularly over time as the brush wears. In contrast,with a brush and wheel, there are no irregularities in the point ofcontact between the brush and wheel. As a result, the spring force usedto maintain contact between the brush and wheel can be reduced, whichalso reduces the drive force or power necessary to move the roboticdevice.

[0055] Still further, the brush and wheel embodiment also reduces trackwear, since the rolling friction between the wheel and track createsless wear than the sliding friction between a brush and power strip. Inthat regard, the conductive strips in a brush and power strip embodimentmust be made sufficiently thick to allow for wear due to brush contactover time. Moreover, as previously noted, spring loading forces forbrushes in a brush and power strip embodiment must be sufficiently highto ensure contact is maintained between the brush and power strip overtime as both wear. A brush and wheel embodiment eliminates theseconcerns and allows for the use of a more inexpensive track having lessstringent design and assembly tolerances.

[0056] In either of the brush and power strip or brush and wheelembodiments, the power strip or conduction rails may be orientedhorizontally, as shown in the Figures, or vertically, or in acombination of both. Indeed, a vertical track orientation may bepreferred, particularly for curved track areas. In that regard, forexample, an extended printed circuit board power strip of the typepreviously described can be easily bent to follow a curved track area ifsuch a power strip is provided with a vertical orientation. In contrast,to follow a curved track with a such a power strip orientedhorizontally, a curved printed circuit board may need to be speciallymanufactured. Moreover, as the radius of curvature of a curved trackarea decreases, skidding and wear of wheels increases on a horizontallyoriented track. This can be alleviated by a vertically oriented track.

[0057] Again in either embodiment, the power conductors or strips may beprovided in segments or sections that can be electrically connectedtogether in a modular fashion, thereby extending the power conductors orstrip substantially throughout a data storage library. Such sections maybe joined together along the path or a guide rail on which a roboticdevice moves in the library. In that regard, it should be noted that ineither embodiment, the segments or sections of power conductors orstrips may be connected in an end to end fashion to provide for roboticdevice movement in a single dimension, or may be connected in agrid-like fashion to provide for robotic device movement in twodimensions and/or to provide power across multiple horizontal paths forrobotic devices, which paths may be stacked vertically on top of eachother, thereby providing for robotic device access to multiple mediacartridge storage cells arranged in a two dimensional configuration ofmultiple rows and columns, such as a planar “wall” or “floor,” or acurved or substantially cylindrical “wall.” Still further, again ineither embodiment, the segments or sections of power conductors orstrips may be connected in such a fashion as to provide for roboticdevice movement in three dimensions.

[0058] When used in such a fashion for power distribution, segmentedpower strips will be sensitive to alignment so as not to create a sloppyjoint. A mis-aligned joint in the power strip may cause a brush to losecontact with a power strip due to bounce. Wear on the brushes and powerstrip pieces at the joints may also cause limited life of the joint.

[0059] As a result, a joint for such power strips is pre-loaded andoverconstrained to cause the power strips in the robot guide rail tosubstantially align. Such a joint preferably includes conductorsslightly longer than the supporting structure of the robot guide rail,so as to force adjoining conductors into contact at their ends as guiderails and conductors are assembled. In addition, adjoining ends ofconductors are preferably beveled or angled such that a force urging theconductors together causes the conductors to slip laterally against eachother, so as to again facilitate alignment at the joint. Such a bevel orangle also spreads out the wiping action of a brush as it traverses thejoint, thereby prolonging the life of the joint and brush, and limitingany problems that may arise as a result of any small offset. Stillfurther, the power strips are preferably pre-loaded or biased by aspring load, thereby causing the joint to stay in compression for thelife of the joint.

[0060] In that regard, referring next to FIGS. 9 through 12a-g, variousperspective, cross-sectional and side views of a power strip and guiderail for use in an automated tape cartridge library. As previouslydescribed, power strip sections in a brush and power strip embodimentmay be sensitive to alignment. As seen in FIGS. 9-12 g, guide railsections (2A, 2B) are designed to accept substantially planar, elongatedpower strip sections (1A, 1B). In that regard, power strip sections (1A,1B) are preferably of the printed circuit board type previouslydescribed, and preferably include upper (56) and lower (not shown)copper conductive layers on opposite surfaces of an FR4 type substratematerial (58). Track alignment pins (50) and holes (52) in guide railsections (2A, 2B) ensure that guide rails sections (2A, 2B) are properlyaligned at the joint, and a joint bolt (54) is provided to ensuresufficient force to maintain the joint. In that regard, an alternativelatch mechanism (55) is depicted in FIGS. 11a and 11 b to providesufficient force to maintain the joint.

[0061] Power strips (1A, 1B) are preferably beveled or angled(preferably at 30°) in a complimentary fashion at adjoining ends so thatsuch ends will move or slide laterally relative to each other in the X-Yplane during assembly of the joint, thereby accounting for varyingtolerances in the lengths of adjoining power strips (1A, 1B) and/orguide rails (2A, 2B). In that same regard, power strips (1A, 1B) arepreferably each provided with spring arms (60), which act as means forbiasing power strips (1A, 1B) together against such lateral motion.Spring arms (60) preferably include mounting pin holes (62) formedtherein, which are designed to align with similar mounting pin holes(64) formed in guide rails (2A, 2B) for receipt of mounting pins (66).Such a configuration facilitates the previously described relativelateral motion between power strips (1A, 1B) in the X-Y plane duringassembly, and helps to ensure that power strips (1A, 1B) remain incontact after assembly. A similar spring arm, mounting pin hole andmounting pin arrangement (67) is preferably provided in a central regionof each power strip (1) and guide rail (2) section (see FIG. 12e).

[0062] Power strips (1A, 1B) are also preferably provided at theiradjoining ends complimentary tongue-and-groove like or dove tail typemating edges or surfaces. Such edges, preferably formed with 45° angles,ensure that power strips (1A, 1B) remain co-planer at the joint (i.e.,refrain from movement relative to each other in the Z direction) so asnot to expose an edge of an upper (56) or lower (not shown) conductivelayer. Electrical connection is provided at the joint through the use ofquick connect electrical slide type connectors (3A, 3B). In that regard,upper (56) and lower (not shown) conductive layers of adjoining powerstrips (1A, 1B) each preferably include an electrical connection point.Upon assembly of power strips (1A, 1B), such electrical connectionpoints are proximate each other such that one connector (3A) creates anelectrical connection between upper conductive layers (56) of adjoiningpower strips (1A, 1B), while the other connector (3B) creates anelectrical connection between lower conductive layers (not shown) ofadjoining power strips (1A, 1B).

[0063] In such a fashion, power strips (1A, 1B) are assembled to createa joint where their respective conductive layers are proximate such thata robotic device having brush or wiper type contacts as previouslydescribed maintains electrical contact therewith as the robotic devicetraverses the joint. A well aligned power strip and guide rail joint isthus provided which facilitates easy movement of a brush or wipercontact thereacross, while at the same time accounting for differingmanufacturing tolerances and expansion rates between the dissimilarmaterials used in the power strips (1) and guide rails (2). It shouldalso be noted that while depicted in the figures in conjunction withprinted circuit type power strips (1), such features may be used withany type of power strip (1) previously described, or with any other typeof joint for power conductors, such as a single conductive strip or busbar. Indeed, many of the above features may also be used with any typeof joint, such as between guide rails without power.

[0064] As is well known in the art, robotic devices in an automated tapecartridge library must be able to communicate with a host controller.This is typically done using multiple conductors (three or more)including power, ground, and signal(s), which can cause many of the samecabling problems previously described. The relatively high cost and lowreliability of conductors and connectors pose a problem for implementinghigh reliability, low cost automated robotic data storage libraries.Such a problem is particularly troublesome if the space available forrouting such conductors is limited.

[0065] Such problems can be overcome by using the oppositely chargedconductive layers of a power strip, power rails, or a cable pair tosupply not only power to the robotic devices, but communication signalsbetween the robotic devices and a controller as well. In that regard, ina brush and power strip embodiment, multiple conductors are particularlyproblematic when power and communication signals need to be sent torobotic devices via the power strip and brushes. Since the reliabilityof the electrical connections in such an embodiment is inherentlyrelatively low, a substantial reliability and complexity penalty may beincurred when multiple conductors are used.

[0066] According to the present invention, a smaller, lower cost andhigher reliability system is made possible by eliminating all conductorsexcept those absolutely needed: power and ground. Information whichwould otherwise be communicated via dedicated signal conductors isinstead modulated onto the power conductor. In such a fashion, thecommunication signals share the same conductor that is used to power therobotic device. Modulator circuits on a controller and the roboticdevices encode the data from the eliminated conductors and impress amodulated signal onto the power conductor. Demodulator circuits on bothends receive and recover the communication signals, translating the databack into its original form. High-speed full-duplex communication isthus implemented without the need for more than two conductorsconnecting the controller and the remote robotic devices.

[0067] Referring now to FIG. 13, a simplified block diagram illustratingdistribution of communication signals to and from robotic devices (72,74) for use in an automated tape cartridge library according to thepresent invention is shown. As seen therein, a power supply (70)provides power to robotic devices (72, 74) via power and groundconductors (76, 78), which are preferably the oppositely chargedconductive layers of a power strip as described in detail above. Acontroller (80), using processor and logic circuits (82), generatessignals for use in controlling the movement and operations of roboticdevices (72, 74). Controller (80) is also provided withmodulator/demodulator circuitry (84) to encode such communicationsignals and impress or superimpose such signals onto the power signalprovided to the robotic devices (72, 74) via the power conductors (76,78). Similar modulator/demodulator circuitry (84) is provided onboardrobotic devices (72, 74) to recover and decode the signals fromcontroller (80). Once recovered and decoded, such signals aretransmitted to motion controller circuitry (86) onboard robotic devices(72, 74) in order to effect the desired movement and operation of therobotic devices (72, 74).

[0068] Robotic devices (72, 74) communicate with controller (80) in thesame fashion, thereby providing feedback to the controller (80)concerning movement and operation of the robotic devices (72, 74), whichinformation the controller (80) may use to generate further controlsignals. As is readily apparent, then, processor and logic circuits(82), and modulator/demodulator circuitry (84) provide means forgenerating the communication signals for transmission between thecontroller (80) and the robotic devices (72, 74) on one of theconductors (76, 78).

[0069] In that regard, such communication signals may be combined withthe power signal in any fashion known in the art. For example, becausepower signals are typically lower frequency signals, communicationsignals may comprise higher frequency signals so that the power signalmay be filtered out by robotic devices (72, 74) and controller (80)using high-pass filters to thereby recover the communication signals. Insuch a fashion, high-speed full duplex communication may be implementedbetween the controller (80) and robotic devices (72, 74) without theneed for multiple conductors, cabling, or wireless connection.

[0070] Electromagnetic interference and unintended signal emissions canbe a problem when transmitting communication signals between roboticdevices and a controller using the oppositely charged conductive layersof a power strip as described above. This can be particularly true forpower conductors that are quite long. Interference from radio,television, and other radio frequency (RF) electromagnetic radiationsources, whether or not intentionally emitted, can interfere with thecommunication signals modulated onto the power conductors. Suchinterference can cause data transmission errors and slow the maximumattainable rate of data transfer.

[0071] In that same regard, when communication signals are modulatedonto a long power conductor, some of the RF energy can radiate throughthe air and interfere with nearby independent power conductors. If thenearby power conductors also contain modulated communication signals,harmful interference can result. The energy radiated by the modulatedpower conductors may also cause interference in radio and televisionbroadcast bands, or other restricted RF bands. Such interference may beprohibited by government regulations.

[0072] According to the present invention, the electromagneticcompatibility (EMC) of the brush and power strip embodiment of thepresent invention is improved by the orientation of the power stripconductors. As will be described in greater detail below, positive andnegative (ground) conductors are preferably separated by a thin layer ofinsulating dielectric. The positive conductor is preferably centeredover the negative conductor. The negative conductor is preferably madewider than the positive conductor in order to minimize fringing of theelectric filed due to the modulated communication signal. The thindielectric minimizes the “loop area” of the conductors. The conductorsthemselves are flat and relatively thin in order to reduce theirrespective surface areas, thereby reducing “skin effect.” All of theabove features serve to improve the EMC of the brush and power stripembodiment.

[0073] Referring next to FIGS. 14 and 15, cross-sectional and top viewsof the power strip for use in an automated tape cartridge libraryaccording to the present invention are shown. As seen therein, oneconductive layer (56), which is shown in the figures as positivelycharged or a power conductor, is preferably provided with a narrowerwidth, w₁, than the width, w₂, of the other conductive layer (57), whichis shown in the figures as negatively charged or a ground conductor. Athin dielectric material (58) is provided between conductive layers (56,57), and has a width, w₂, that is preferably substantially equal to thatof conductive layer (57). While not required, conductive layer (56) ispreferably centered on the surface of one side of dielectric material(58) relative to the width, w₂, of conductive layer (57), and thus atequal distances, x, from the edges of dielectric material (58) sincedielectric material (58) has substantially the same width, w₂, asconductive layer (57). In that regard, as previously described,conductive layers (56, 57) are preferably copper. Dielectric material(58) preferably has a low dielectric constant, k, such as FR4 previouslydescribed, or Teflon.

[0074] The above-described configuration serves to improve theelectromagnetic compatibility (EMC) of the power strip. Moreparticularly, the different widths of the conductive layers (56, 57)help to minimize fringing of the electric field due to the modulatedcommunication signals. In that regard, the greater the distance x can bemade, either by narrowing conductive layer (56) or by wideningconductive layer (57) and dielectric (58), the greater the beneficialeffect on fringing. Conductive layers (56, 57) should, however, maintainsufficient width to allow adequate contact with brushes (6) in order tosupply power to a robotic device.

[0075] Moreover, as is well known in the art, electrical current isgenerally forced to the outside surfaces of a conductor, particularly athigher frequencies. Conductors having less surface area therefore havehigher resistance, a phenomenon generally referred to as “skin effect.”By making conductive layers (56, 57) generally flat and thin, moresurface area is created, thereby reducing resistance for the higherfrequency communication signals. Such lowered resistance in turn reducedsignal loss, thereby allowing for the use of longer tracks, while at thesame time improving signal integrity by providing better immunity frominterference by other signals.

[0076] Still further, a thin dielectric (58) helps to minimize the “looparea” of the conductors (56, 57). In that regard, FIGS. 16a and 16 b area cross-sectional view and a simplified electrical schematic,respectively, of the power strip for use in an automated tape cartridgelibrary according to the present invention. As seen therein, conductors(56, 57) are connected through a power supply (90) and a load (92),thereby creating a loop. While the length, l, of conductors (56, 57) isgenerally fixed, the thickness, t, of the dielectric (58) therebetweenmay be adjusted. That is, while the length of the loop is generallyfixed, its height is adjustable. A thin dielectric (58) thus helps toreduce “loop area.”

[0077] As previously noted, by minimizing fringing, “skin effect” and“loop area,” the above-described configuration improves electromagneticcompatibility (EMC). In general, the above-described power rail presentsa low impedance, thereby reducing coupling from interfering signals. Inparticular, minimizing fringing reduces the possibility that acommunication signal on a power rail will interfere with other devices,including other power rails carrying other communication signals.Minimizing “skin effect” and “loop area” also reduces the possibility ofsuch radiation type interference.

[0078] In a power line communication system such as described above,signal reflections can pose a significant signal integrity problem.Reflections can destructively interfere with the communication signal,particularly when the length of the power line is long compared to thewavelength of the carrier signal. The reflection problem can bemitigated with the addition of line terminators at the extreme ends ofthe power line. In that regard, FIG. 17 is a simplified electricalschematic diagram illustrating a termination scheme for a line in apower strip or rail communication system according to the presentinvention. As seen therein, the termination scheme comprises twoparallel terminators (90, 91) at each of the two ends of the powerline/rail (92). As shown in FIG. 17, each terminator (90, 91) preferablycomprises an RC termination, although those of ordinary skill willappreciate that a variety of termination schemes could be employed toachieve the same effect.

[0079] Still referring to FIG. 17, series terminators (93, 94), whichare preferably resistors, are also preferably provided on the output ofeach modulator circuit (95) for both the controller (96) and theautomated robot, or handbot (97). The combination of series terminationand parallel termination further enhances the signal integrity of thepower line (92). Either series or parallel termination could be used onits own, however. Proper line termination such as that depicted in FIG.17 dramatically improves signal integrity and increases the maximumattainable rate of data transfer as well as extending the maximum lengthof the conductors.

[0080] Referring now to FIG. 18, a simplified, exemplary flowchart ofthe method of the present invention is shown, denoted generally byreference numeral 100. The method (100) is provided for use in a datastorage library having a plurality of cells for holding media cartridgesfor use in storing data, at least one media drive, a robotic device fortransporting cartridges between the plurality of cells and the at leastone media drive in the data storage library, and a controller forcontrolling the robotic device, a method for transmission ofcommunication signals between the controller and the robotic device. Asseen in FIG. 18, the method (100) comprises providing (102) asubstantially planar electrical insulator having opposed first andsecond sides, providing (104) a first substantially planer electricalconductor on the first side of the insulator for use in providingelectrical power to the robotic device, the first conductor to beprovided with an electrical charge and having a width, and providing(106) a second substantially planar electrical conductor on the secondside of the insulator for use in providing electrical power to therobotic device, the second conductor to be provided with an electricalcharge opposite the electrical charge of the first conductor, the secondconductor having a width. The method further comprises providing (108)means for generating the communication signals for transmission betweenthe controller and the robotic device on one of the first and secondconductors, wherein the width of the second conductor is less than thewidth of the first conductor, and the second conductor is substantiallycentered on the second side of the insulator relative to the width ofthe first conductor to reduce fringing of an electromagnetic fieldresulting from a transmitted communication signal.

[0081] It should be noted that the simplified flowchart depicted in FIG.18 is exemplary of the method of the present invention. In that regard,the steps of such method may be executed in sequences other than thoseshown in FIG. 18, including the execution of one or more stepssimultaneously.

[0082] Thus it is apparent that the present invention provides forimproved system and method for transmitting communication signalsbetween a controller and a robotic device in a data storage library. Asis readily apparent from the foregoing description, the system andmethod of the present invention improve the electromagneticcompatibility (EMC) of brush and strip power distribution by theorientation of the power strip conductors. More particularly, the systemand method of the present invention employ positive and negative(ground) conductors preferably separated by a thin layer of insulatingdielectric. The positive conductor is preferably centered over thenegative conductor, and the negative conductor is preferably wider thanthe positive conductor in order to reduce fringing of the electric fileddue to the modulated communication signal. The thin dielectric reducesthe “loop area” of the conductors. The conductors themselves aresubstantially flat and relatively thin in order to reduce theirrespective surface areas, thereby reducing “skin effect.”

[0083] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andit is understood that various changes may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. In a data storage library having a plurality ofcells for holding media cartridges for use in storing data, at least onemedia drive, a robotic device for transporting cartridges between theplurality of cells and the at least one media drive in the data storagelibrary, and a controller for controlling the robotic device, a systemfor transmission of communication signals between the controller and therobotic device, the system comprising: a substantially planar electricalinsulator having opposed first and second sides; a first substantiallyplaner electrical conductor on the first side of the insulator for usein providing electrical power to the robotic device, the first conductorto be provided with an electrical charge and having a width; a secondsubstantially planar electrical conductor on the second side of theinsulator for use in providing electrical power to the robotic device,the second conductor to be provided with an electrical charge oppositethe electrical charge of the first conductor, the second conductorhaving a width; and means for generating the communication signals fortransmission between the controller and the robotic device on one of thefirst and second conductors, wherein the width of the second conductoris less than the width of the first conductor, and the second conductoris substantially centered on the second side of the insulator relativeto the width of the first conductor to reduce fringing of anelectromagnetic field resulting from a transmitted communication signal.2. The system of claim 1 wherein each of the first and second conductorscomprises an elongated conductive strip, and the insulator comprises anelongated member provided with a thickness sufficient to minimize a looparea associated with the elongated first and second conductors.
 3. Thesystem of claim 2 wherein the first and second conductors and theinsulator together comprise a power distribution strip, and wherein aplurality of power distribution strips are electrically connected fortransmission of electrical power and communication signals substantiallythroughout the data storage library to the robotic device.
 4. The systemof claim 1 wherein the communication signals comprise high frequencysignals, and the first and second conductors are provided a surface areasufficient to reduce a skin effect associated with the transmission ofthe high frequency communication signals.
 5. The system of claim 4wherein the means for generating the communication signals comprisesmodulator/demodulator circuitry associated with the host controller, andmodulator/demodulator circuitry provided on the robotic device, themodulator/demodulator circuitry for encoding and transmittingcommunication signals on one of the first and second conductors and forreceiving and decoding transmitted communication signals.
 6. The systemof claim 5 wherein the first and second conductors are for transmittinga power signal to the robotic device, the power signal having a lowerfrequency than the high frequency communication signals, and wherein themodulator/demodulator circuitry comprises a high-pass filter forrecovering the high frequency communication signals from the lowerfrequency power signal.
 7. The system of claim 1 wherein the insulatorcomprises a material having a low dielectric constant.
 8. The system ofclaim 1 wherein each of the first and second conductors comprisescopper.
 9. The system of claim 3 wherein the plurality of electricallyconnected power strips has an end point, the end point being providedwith a terminator in electrical communication with the plurality ofelectrically connected power strips for reducing reflection of thetransmitted communication signals, the terminator comprising a resistorand capacitor.
 10. The system of claim 3 wherein the robotic device isprovided with electrical contacts for making sliding electrical contactwith the first and second conductors.
 11. In a data storage libraryhaving a plurality of cells for holding media cartridges for use instoring data, at least one media drive, a robotic device fortransporting cartridges between the plurality of cells and the at leastone media drive in the data storage library, and a controller forcontrolling the robotic device, a system for transmission ofcommunication signals between the controller and the robotic device, thesystem comprising: a substantially planar electrical insulator havingopposed first and second sides; a first substantially planer electricalconductor on the first side of the insulator for use in providingelectrical power to the robotic device, the first conductor to beprovided with an electrical charge and having a width; a secondsubstantially planar electrical conductor on the second side of theinsulator for use in providing electrical power to the robotic device,the second conductor to be provided with an electrical charge oppositethe electrical charge of the first conductor, the second conductorhaving a width; and means for generating the communication signals fortransmission between the controller and the robotic device on one of thefirst and second conductors, wherein each of the first and secondconductors comprises an elongated conductive strip, and the insulatorcomprises an elongated member provided with a thickness sufficient tominimize a loop area associated with the elongated first and secondconductors.
 12. In a data storage library having a plurality of cellsfor holding media cartridges for use in storing data, at least one mediadrive, a robotic device for transporting cartridges between theplurality of cells and the at least one media drive in the data storagelibrary, and a controller for controlling the robotic device, a methodfor transmission of communication signals between the controller and therobotic device, the method comprising: providing a substantially planarelectrical insulator having opposed first and second sides; providing afirst substantially planer electrical conductor on the first side of theinsulator for use in providing electrical power to the robotic device,the first conductor to be provided with an electrical charge and havinga width; providing a second substantially planar electrical conductor onthe second side of the insulator for use in providing electrical powerto the robotic device, the second conductor to be provided with anelectrical charge opposite the electrical charge of the first conductor,the second conductor having a width; and providing means for generatingthe communication signals for transmission between the controller andthe robotic device on one of the first and second conductors, whereinthe width of the second conductor is less than the width of the firstconductor, and the second conductor is substantially centered on thesecond side of the insulator relative to the width of the firstconductor to reduce fringing of an electromagnetic field resulting froma transmitted communication signal.
 13. The method of claim 12 whereineach of the first and second conductors comprises an elongatedconductive strip, and the insulator comprises an elongated memberprovided with a thickness sufficient to minimize a loop area associatedwith the elongated first and second conductors.
 14. The method of claim13 wherein the first and second conductors and the insulator togethercomprise a power distribution strip, and wherein a plurality of powerdistribution strips are electrically connected for transmission ofelectrical power and communication signals substantially throughout thedata storage library to the robotic device.
 15. The method of claim 12wherein the communication signals comprise high frequency signals, andthe first and second conductors are provided a surface area sufficientto reduce a skin effect associated with the transmission of the highfrequency communication signals.
 16. The method of claim 15 wherein themeans for generating the communication signals comprisesmodulation/demodulation circuitry associated with the host controller,and modulator/demodulator circuitry provided on the robotic device, themodulator/demodulator circuitry for encoding and transmittingcommunication signals on one of the first and second conductors and forreceiving and decoding transmitted communication signals.
 17. The methodof claim 16 wherein the first and second conductors are for transmittinga power signal to the robotic device, the power signal having a lowerfrequency than the high frequency communication signals, and wherein themodulator/demodulator circuitry comprises a high-pass filter forrecovering the high frequency communication signals from the lowerfrequency power signal.
 18. The method of claim 12 wherein the insulatorcomprises a material having a low dielectric constant.
 19. The method ofclaim 12 wherein each of the first and second conductors comprisescopper.
 20. The method of claim 14 wherein the plurality of electricallyconnected power strips has an end point, the end point being providedwith a terminator in electrical communication with the plurality ofelectrically connected power strips for reducing reflection of thetransmitted communication signals, the terminator comprising a resistorand capacitor.
 21. The method of claim 14 wherein the robotic device isprovided with electrical contacts for making sliding electrical contactwith the first and second conductors.
 22. In a data storage libraryhaving a plurality of cells for holding media cartridges for use instoring data, at least one media drive, a robotic device fortransporting cartridges between the plurality of cells and the at leastone media drive in the data storage library, and a controller forcontrolling the robotic device, a method for transmission ofcommunication signals between the controller and the robotic device, themethod comprising: providing a substantially planar electrical insulatorhaving opposed first and second sides; providing a first substantiallyplaner electrical conductor on the first side of the insulator for usein providing electrical power to the robotic device, the first conductorto be provided with an electrical charge and having a width; providing asecond substantially planar electrical conductor on the second side ofthe insulator for use in providing electrical power to the roboticdevice, the second conductor to be provided with an electrical chargeopposite the electrical charge of the first conductor, the secondconductor having a width; and providing means for generating thecommunication signals for transmission between the controller and therobotic device on one of the first and second conductors, wherein eachof the first and second conductors comprises an elongated conductivestrip, and the insulator comprises an elongated member provided with athickness sufficient to minimize a loop area associated with theelongated first and second conductors.